Corticobulbar tract. And that includes these upper motor neuron axons that are going to innervate lower motor neurons in the brain stem and because the wiring is a little bit more complicated in the brain stem, we can get some different patterns of weakness with abnormalities of this pathway.
Activity theory (AT; Russian: ÑÐµÐ¾ÑÐ¸Ñ Ð´ÐµÑÑÐµÐ»ÑÐ½Ð¾ÑÑÐ¸) is an umbrella term for a line of eclectic social sciences theories and research with its roots in the Soviet psychological activity theory pioneered by Lev Vygotsky, Alexei Leont'ev and Sergei Rubinstein.
Systems theory. Systems theory or systems science is the interdisciplinary study of systems. A system is an entity with interrelated and interdependent parts; it is defined by its boundaries and it is more than the sum of its parts (subsystem). Changing one part of the system affects other parts and the whole system, with predictable patterns of behavior.